Project Abstract: Research suggests that fathers who maintain supportive couple relationships with their children?s mothers before and after their pregnancy have a greater likelihood of continued engagement with their children, and stronger relationships with their families (Pinzon & Jones, 2012); however, little is known about the development of teenage parents? couple or co-parenting relationships across children?s early development or parents? transition to young adulthood, when developing brains are especially receptive to intervention. This dissertation will be the first to examine the development of teenage parents? supportive couple and co-parenting relationships across the first nine years of parenthood, how these relationships link to maternal parenting behaviors and children?s mental health, and whether maternal residential contexts moderate these effects. Latent growth modeling will be used to identify timepoints, relationships, and residential contexts that are critical to the development of teenage mothers? responsive parenting behaviors and their children?s mental health. Insights from this dissertation will help to inform healthy marriage and family support programs looking to implement innovative program components for teenage couples and recruitment strategies for complex families. A subsample of children who were born to mothers nineteen years old or younger will be extracted from the Fragile Families and Child Wellbeing (FFCW) database. Only children who reside with their mothers and have data reported from biological fathers at baseline and one other timepoint will be maintained.